No Ordinary Meteor Shower

An asteroid spawns the Geminids

By J. Alex Knoll

Thursday’s new moon provides dark cover for this year’s Geminid meteor shower, which peaks that night and into the wee hours Friday. The Geminids are perhaps the best of the annual meteor showers, but because of December’s chill, many people haven’t truly appreciated them.
The Geminids put on a great show, often delivering 60 meteors an hour under dark skies. But in 1996, another year when the shower coincided with new moon, skywatchers with clear skies could see more than 100 meteors an hour! Even with mild urban glare, you can expect up to see 20 in a given hour. They’re bright and colorful, often leaving lingering trails in their wake.
The Geminids start early, well before midnight. Most meteor showers don’t gear up until closer to dawn. These begin as the constellation ­Gemini rises in the east around sunset and continue until sunrise, by which time the Twins stand above the west horizon. And while the meteors appear to originate from the golden star Castor, you’re likely to spot them anywhere on the celestial dome.
Finally, the Geminids are unique. Whereas other meteors are born of comets, these are the product of an asteroid. Accounts of the Geminids only begin in 1862. For more than 100 years astronomers searched the heavens for the parent comet. Then, in 1983 a NASA satellite discovered the asteroid 3200 Phaethon and determined it to be the parent of the Geminids. Both asteroids and comets are from the infancy of our solar system 4.5 billion year ago. Asteroids, however, formed closer to the sun and are made up primarily of rock and metal. Comets formed farther out and are composed of ice, dust and rock. With no melting ice to create a tail, astronomers are still puzzled what created 3200 Phaeton’s debris trail. One hypothesis is that the asteroid was struck by another interstellar object and has been losing material ever since.